Residential Roof Penetrations Cannot Be Used On Commercial Roofs – Part II

Why Residential Roofs Penetrations Can’t Be Used On Commercial Buildings?

In a very recent blog article about residential roof penetrations, we took a look at the problems associated with installing residential vent terminations on commercial roofs. In this case, we’re  referring to and classify residential building roofs as commercial if the roofs are low slope or flat rooftops.    We specifically classify rooftops in this hierarchy because even in the case of residential row homes, when the rooftop is flat the roof system used is a commercial product and must follow the rules related to installation of that commercial system. 

The picture below shows an air vent installed on a shingle roof. We took a look at this particular exhaust termination in the last article, but in this particular picture you can see the termination more closely and the bottom of the flange is visible. that flange covers the top of the shingles below.

air vent on shingle roof

At other parts of the roof, other terminations stand up high above the roof membrane itself. The two pipes standing up are plumbing vent pipes. same as in commercial systems, it’s important to keep these pipes in all pipes or penetrations through the roof above the roof membrane because of snow loads in our  geographic area of Washington DC or Capitol Hill.

terminations above roof membrane residential roof penetrations

The next picture below shows the low slope or flat roof of the building we looked at in our last article. You can notice that the coping above or on top of the parapet at the demising or exterior wall of the building has fasteners or bolts driven through the horizontal or top portion of the metal coping.  Fasteners should be never driven through the top of metal coping. It’s a potential source of leakage and it’s not necessary. If properly installed, coping can be mounted with fasteners through the vertical sides instead of through the top.

low slope parapet

As a point of comparison, another roof is shown in the next picture below. This particular roof is also a flat or low slope modified bitumen roof membrane, but the membrane itself runs up and over the top of the parapet wall without a terminating coping. This is also not correct, a metal or similar material coping should be installed on top of each parapet, but in this case it’s almost possibly better that they didn’t install the coping because it’s better to not have fasteners driven through the horizontal portion of the coping.

low slope modified bitumen roof

For reference, a closer view of the coping metal with fasteners driven through the horizontal portion of the top of the coping follows below. This is an incorrect installation.

coping metal

How To Maintain A Flat Roof System

Smart proactive replacement, construction, upkeep and maintenance of low slope roof systems requires an enthusiastic interest and understanding of waterproofing principles and building science.   Here in Washington DC, historic and modern residential and commercial buildings are extremely expensive and the roof and related systems provide the shield that preserves the building. 

We encourage all of our clients, and all readers of this article and to our blog in general, to prioritize the value of quality construction and building maintenance, and develop a relationship with our company.  You can learn a lot more on our blog.  Feel free to check it out.  If you have questions about the roof and related systems of your building in Washington DC, contact us or fill out the webform below and drop us a line.  We will be in touch if we can help.

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